What are good examples for major and minors NC?
If you're talking internal audits, then there are none. Either something is conforming or it is not. The actions taken to eliminate the root cause of that "something" should be evaluated for effectiveness through your own internal processes - I would leave grading to the CB's.
On a related note - I have witnessed many customer audits and never once did they refer to anything they found as a "major" or "minor" - they simply informed us what they found that we needed to correct, and gave us a timetable to fix those issues, based on severity or sometimes just based on gut. From a customer's standpoint (at least the ones I've been involved with), they really don't invest too much of their time calling NC's "this or that" but they are nevertheless cognizant of the risks encountered, should those issues continue to remain unaddressed.
Brian